System and method for releasing user equipment context by a home gateway

ABSTRACT

A communication system is described in which a handover procedure is provided to allow a mobile device to transfer from a home base station connected to a core network via a home base station gateway to another base station not coupled via the home base station gateway. A novel extension to the handover procedure is provided in which the home base station gateway is informed of the transfer of the mobile device, allowing context and resources assigned to the mobile device at the base station gateway to be released.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a Continuation of U.S. application Ser. No.13/818,090 filed Feb. 20, 2013, which is a National Stage ofInternational Application No. PCT/JP2012/054177 filed Feb. 15, 2012, andclaims priority from United Kingdom Patent Application No. 1102883.4filed Feb. 18, 2011, the disclosures of which are incorporated byreference herein in their entirety.

TECHNICAL FIELD

The present invention relates to mobile telecommunication networks,particularly but not exclusively networks operating according to the3^(rd) Generation Partnership Project (3GPP) standards or equivalents orderivatives thereof. The invention has particular although not exclusiverelevance to the management of the handover of a mobile device from onebase station to another.

BACKGROUND ART

Under the 3GPP standards, a NodeB (or an eNB in LTE) is the base stationvia which mobile devices connect to the core network. Recently the 3GPPstandards body has adopted an official architecture and started work ona new standard for home base stations (HNB). Where the home base stationis operating in accordance with the (Long Term Evolution) LTE standards,the HNB is sometimes referred to as a HeNB. A similar architecture willalso be applied in the WiMAX network. In this case, the home basestation is commonly referred to as a femto cell. For simplicity, thepresent application will use the term HeNB to refer to any such homebase station and will use the term NodeB generically to refer to otherbase stations (such as the base station for the macro cell in which aHeNB operates). The HeNB will provide radio coverage (for example,3G/4G/WiMAX) within the home, small and medium enterprise, shoppingMalls etc and will connect to the core network via a suitable publicnetwork (for example via an ADSL link to the Internet) or operatornetwork and in the case of the 3GPP standards, via an optional HeNBgateway (HeNB-GW) which typically will aggregate traffic from severalHeNBs.

For a HeNB connected behind a HeNB gateway, two pairs of mobiletelephone associated connections are established, one between the HeNBand the HeNB gateway, and another between the HeNB gateway and themobile management entity (MME) within the core network. Mapping betweenthe two contexts associated with a specific mobile telephone isperformed by the HeNB gateway, and therefore for a single mobiletelephone connected to a HeNB behind a HeNB gateway, context andresources are allocated at both the HeNB and the HeNB gateway.

In common with other NodeBs, HeNBs are able to communicate with eachother (and other NodeBs) using the X2 interface. In particular, heNBsare able to coordinate a handover process between source and target basestations using the X2 interface without overall control by the corenetwork. During an X2 based handover between two HeNBs, the target HeNBexplicitly releases the UE context at the source HeNB using the X2AP UEContext Release procedure. However, as the X2 interface is used tocoordinate the handover, for a source HeNB behind a HeNB gateway, nomessage relating to release of the UE context traverses through the HeNBgateway, and therefore the HeNB gateway does not have any means tounderstand the mobile telephone has been handed over via an X2 basedhandover to the target HeNB.

SUMMARY OF THE INVENTION

Thus, according to the present handover processes, whenever an X2 basedhandover takes place where a source HeNB is behind a HeNB gateway, andthe target HeNB is not behind the same HeNB gateway, the UE context andrelated resources assigned by the HeNB gateway to the mobile telephonewill not be released. Thus, there exists a need to adapt the currentprocesses to overcome this problem.

Although for efficiency of understanding for those of skill in the art,the invention will be described in detail in the context of a 3G system(UMTS, LTE), the principles of the invention can be applied to othersystems (such as WiMAX) in which mobile telephones or User Equipment(UE) communicate with one of several base stations with thecorresponding elements of the system changed as required.

Accordingly, preferred embodiments of the present invention aim toprovide methods and apparatus which overcome or at least alleviate theabove issues.

According to a first aspect of the invention, there is provided a basestation for communicating with a plurality of mobile devices and coupledto a core network via a home base station gateway, the base stationcomprising a connection management module configured to perform ahandover process and comprising means for transferring a communicationlink associated with a mobile device from the base station to anotherbase station, the other base station coupled to the core network otherthan via the home base station gateway; means for receiving a messagefrom the other base station indicating that handover has been completed,and means operable in response to receiving the message indicating thathandover has been completed to send an indication to the home basestation gateway that the mobile station is no longer coupled to the basestation.

The base station may comprise a home base station, for example a HeNB,and the home base station gateway may comprise a HeNB gateway forconnecting the HeNB to the core network.

The means for transferring a communication link to another base stationmay comprise means for transferring the communication link to a furtherhome base station, or further HeNB. The further HeNB may be coupled tothe core network via a different home base station gateway, or HeNB gateway.

The means for transferring a communication link to another base stationmay further comprise means for transferring the communication link to amacro cell associated with the other base station, for example an eNB.

The handover process may comprise a X2 based handover procedure, and themessage indicating that handover has been completed may comprise a X2 UEContext Release message.

According to a further aspect of the invention, there is provided amethod of facilitating handover in a communications network, the methodcomprising performing a handover of a mobile device from a source basestation coupled to a core network via a base station gateway to a targetbase station coupled to the core network other than via the base stationgateway, receiving a message from the target base station indicatingthat handover has been completed, and in response to receiving themessage indicating that handover has been completed, sending anindication to the base station gateway that the mobile station is nolonger coupled to the base station.

According to a further aspect of the invention, there is provided a homebase station gateway for communicating with a plurality of base stationsand coupled to a core network, the base station gateway comprising amobile telephone registration module configured to receive an indicationfrom a base station coupled to the base station gateway that acommunication link associated with a mobile device has been transferredfrom the base station to a further base station and further configuredto release a context associated with the mobile device in response toreceiving the indication.

The further base station is not coupled to the core network via the basestation gateway, for example the further base station may be directlycoupled to the core network or may be coupled via a different home basestation gateway.

The transfer of the communication link may comprise an X2 based handoverprocedure. The base station may be a home base station, such as a HeNB.

According to a further aspect of the invention, there is provided amethod of facilitating handover in a communications network, the methodcomprising receiving at a base station gateway an indication from a basestation coupled to the base station gateway that a communication linkassociated with a mobile device has been transferred from the basestation to a further base station, and in response to receiving theindication, releasing a context associated with the mobile station.

According to a further aspect of the invention, there is provided a homebase station gateway for communicating with a plurality of base stationsand coupled to a core network, the base station gateway comprising amobile telephone registration module configured to identify a pathswitch request from a base station, the path switch request associatedwith a communication link transferred to the base station, the mobiletelephone registration module further configured to assign a context toa mobile device associated with the communication link in response toidentifying the path switch request.

The base station may be a home base station such as an HeNB, and may becoupled to the core network via the base station gateway. The transferof the communication link to the base station may comprise an X2 basedhandover procedure.

According to a further aspect of the invention, there is provided a basestation for communicating with a plurality of mobile devices and coupledto a core network via a home base station gateway, the base stationcomprising a connection management module configured to perform ahandover process comprising: transferring a communication linkassociated with a mobile device to the base station from another basestation, the other base station coupled to the core network other thanvia the home base station gateway, the handover process furthercomprising receiving a message from the other base station providinginformation identifying the mobile device, and storing the informationidentifying the mobile device at the base station.

The base station may comprise a home base station, for example a HeNB.The transfer of the communication link may comprise an X2 based handoverprocedure.

The information identifying the mobile device comprises an MME UE S1APID value.

According to a further aspect of the invention, there is provided a userequipment adapted to operate with a base station as described above.

According to a further aspect of the invention, there is provide acomputer program product comprising computer program code configured toperform any of the above described methods.

According to a further aspect of the invention, there is provided a basestation for communicating with a plurality of mobile devices and coupledto a core network via a home base station gateway, the base stationcomprising a connection management module configured to perform ahandover process comprising transferring a communication link associatedwith a mobile device from the base station to another base station, theother base station coupled to the core network other than via the homebase station gateway, the handover process further comprising receivinga message from the other base station indicating that handover has beencompleted, and in response to receiving the message indicating thathandover has been completed sending an indication to the home basestation gateway that the mobile station is no longer coupled to the basestation.

According to a further aspect of the invention, there is provided a basestation for communicating with a plurality of mobile devices and coupledto a core network via a home base station gateway, the base stationcomprising a connection management module configured to perform ahandover process and comprising means for transferring a communicationlink associated with a mobile device to the base station from anotherbase station, the other base station coupled to the core network otherthan via the home base station gateway; means for receiving a messagefrom the other base station providing information identifying the mobiledevice, and means for storing the information identifying the mobiledevice at the base station.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the invention will now be described, by way of example,with reference to the accompanying drawings in which:

FIG. 1 schematically illustrates a mobile telecommunication system;

FIGS. 2a and 2h schematically illustrate hand over scenarios in themobile telecommunication system of FIG. 1;

FIG. 3 is a block diagram of a home eNB forming part of the system shownin FIG. 1;

FIG. 4 is a block diagram of a home base station gateway forming part ofthe system shown in FIG. 1;

FIG. 5 is a timing diagram indicating a handover procedure by whichcommunication with a mobile telephone is transferred between a sourceand target home base station;

FIG. 6 is a timing diagram indicating a handover procedure by whichcommunication with a mobile telephone is transferred between a sourceand target home base station served by different serving gateways in thecore network;

FIG. 7 schematically illustrates a further hand over scenario in themobile telecommunication system of FIG. 1; and

FIG. 8 is a timing diagram indicating a portion of the handoverprocedure of FIG. 5.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS

Overview

FIG. 1 schematically illustrates a mobile (cellular) telecommunicationsystem 1 in which a user of a mobile telephone 3 can communicate withother users (not shown) via a ‘home’ base station (HeNB) 11-1, which hemay be permitted to access. The HeNB 11-1 is coupled via a home basestation gateway (HeNB-GW) 15, to the core telephone network 8 includingmobile management entity/serving gateway (MME/S-GW) 6-1. In thetelecommunication system 1 the user may also communicate with the otherusers (not shown) via an HeNB 11-2 which, in this example, is alsocoupled via the same home base station gateway (HeNB-GW) 15, to themobile management entity/serving gateway 6-1.

In the example of FIG. 1, the HeNBs 11-1 and 11-2 connect to a commonHeNB-GW 15 via a suitable network connection such as an ADSL or cableconnection providing an Internet connection and are programmed with theIP address of the HeNB-GW 15 so that all uplink communications aretransmitted via HeNB-GW 15. HeNB 11-3 provides a further cell area inwhich a user may connect via HeNB 11-3 and a suitable interactconnection such as an ADSL or cable connection to a mobile managemententity/serving gateway 6-2 without connecting to HeNB-GW 15. It is notedthat while HeNB 11-3 is shown as connecting to a different MME/S-GW 6-2than HeNBs 11-1 and 11-2, HeNB 11-3 could connect to the same MME/S-QW6-1 without connecting via HeNB GW 15.

As is well known, a mobile telephone 3 may be transferred from a cellassociated with a first HeNB 11-2 to a second cell associated with asecond HeNB 11-3. The process of performing the handover HO isillustrated schematically in FIG. 1 and described in more detail belowwith reference to FIG. 6. The MME 6-1, and/or MME 6-2, keeps track ofmobile devices and their connections to the base stations as they movethrough the network in a database of Mobility Management Entity (MME)and Evolved Packet System (EPS) bearer contexts.

FIGS. 2a and 2b show further handover scenarios in which context andresources allocated to a mobile station at the HeNB gateway 15 may notbe released after an X2 based handover of the mobile station 3.

In the scenario illustrated in FIG. 2a , mobile telephone 3 istransferred from a cell associated with source HeNB 11-2 to target HeNB11-3. In this case, source HeNB 11-2 is coupled to the core network 8via a first HeNB GW 15-1, while target HeNB 11-3 is connected to thecore network 8 via HeNB GW 15-2.

The scenario illustrated in FIG. 2b is similar to the handover scenarioof FIG. 1, except that the target base station comprises eNB 13, ratherthan a further HeNB. Some implementations of the telecommunicationnetwork 1 may allow such handovers to take place, and in suchimplementations the problem addressed by embodiments of the inventionwill manifest.

In each of the handover scenarios illustrated in FIGS. 1, 2 a and 2 b,embodiments of the invention provide a method of facilitating release ofcontext and resources assigned to a mobile telephone 3 at the HeNBgateway 15-1 when an X2 based handover procedure is used to handovermobile telephone from a source HeNB coupled to the core network 8 viathe HeNB gateway 15-1 to a target base station that is not coupled viathe same HeNB gateway 15-1.

As will be, recognized by the skilled person, core network 8 may includemany other entities and modules required to provide the communicationnetwork 1, which have not been shown in the figures to aid clarity. Suchentities include the packet data network (PDN) gateway for routingpacket data to a mobile device.

Home Base Station (HeNB)

FIG. 3 is a block diagram illustrating the main components of one of thehome base stations (HeNB) 11 shown in FIG. 1. As shown, the HeNB 11includes transceiver circuitry 51 which is operable to transmit signalsto, and to receive signals from, the mobile telephone 3 via one or moreantennae 53 and which is operable to transmit signals to and to receivesignals from the HeNB-GW 15 via an HeNB-GW interface 55. The operationof the transceiver circuitry 51 is controlled by a controller 57 inaccordance with software stored in memory 59. The software includes,among other things, art operating system 61, a base station registrationmodule 63, a mobile telephone registration module 65, and a connectionmanagement module 67.

The base station registration module 63 is operable to register the HeNBwith the HeNB-GW 15 and the telephone registration module 65 is operableto register the user equipment 3 with the HeNB 11 and with the HeNB-GW15. The connection management module 67 is operable to manage theconnections of mobile telephones camped on the cell of the HNB 11 and tobroadcast system information relating to the cell to mobile telephones 3in the vicinity.

On conclusion of a successful handover of a mobile telephone, theconnection management module 67 of a target HeNB 11 is configured totransmit a message to inform the source HeNB to release context andresources associated with the mobile telephone. Upon receipt of thismessage, the mobile telephone registration module 65 is operable torelease the context and resources associated with the handed over mobiletelephone.

HeNB Gateway (GW)

FIG. 4 is a block diagram illustrating the main components of the HeNBgateway (HeNB-GW) 15 shown in FIG. 1. As shown, the HeNB-GW 15 includesa transceiver circuit 101 which is operable to transmit signals to, andto receive signals from, the HeNB 11-1, 11-2 via the HeNB interface 103and which is operable to transmit signals to and to receive signals fromthe MME/S-GW 6 in the core network 8 via a core network interface 105.The operation of the transceiver circuit 101 is controlled by acontroller 107 in accordance with software stored in memory 109. Thesoftware includes, among other things, an operating system 111, a HeNBregistration module 113, and a mobile telephone registration module 115.The HeNB registration module 113 is operable to control the registrationof HeNBs 11-1, 11-2 with the gateway and the mobile telephoneregistration module 115 is operable to control the registration of theuser equipment 3 and to perform access control as required.

The mobile telephone registration module is further operable to receivean indication from a home base station connected to the core network 8via the home base station gateway, that a user equipment previouslyconnected to the base station, and therefore having a context registeredat the home base station gateway, has been handed over to a target basestation not coupled to the home base station gateway. In response toreceiving the indication that the user equipment has been handed over,the mobile telephone registration module is operable to release thecontext and resources associated with the user equipment 3.

X2 Based Handover

An X2 based handover of a mobile telephone 3 between home base stations11-2 and 11-3 illustrated in FIGS. 1, 2 a, and 2 h will now bedescribed, by way of example only, with reference to the timing diagramof FIG. 5.

As those skilled in the art will appreciate, the X2 interface is theinterface via which base stations communicate with each other. In an X2based handover the handover process is coordinated between the sourceand target base stations without overall control by the core network 8.X2 based handover is therefore advantageous as it reduces load on thecore network 8.

As shown in FIG. 5, once a mobile telephone 3 establishes communicationwith a source HeNB 11-2 the source HeNB 11-2 relays packet data betweenthe mobile telephone 3 and the MME/S-GW 6-1 of the core network 8 (viathe HeNB-GW 15). During communication between the mobile telephone 3 andsource HeNB 11-2 properties of the communication between the mobiletelephone 3 and the HeNB 11-2 and other base stations are measured toassist in control of the mobile telephone's connection mobility. TheHeNB 11-2 is operable to trigger the mobile telephone 3 to send ameasurement report to the HeNB 11-2.

Based on the measurement report information and/or other radio resourcemanagement (RRM) information, the source HeNB 11-2 can determine whetheror not to hand the mobile telephone 3 off to a target HeNB 11-3. In theevent that it is determined that the mobile telephone 3 is to be handedoff to a target HeNB 11-3, the source HeNB 11-2 transmits a handoverrequest 42 to the target HeNB 11-3 which includes information necessaryfor the target HeNB 11-3 to prepare the handover, such as informationrelating to quality of service and other parameters.

The target HeNB 11-3 may perform admission control functions dependenton the received information and, if the necessary resources can begranted by the target HeNB 11-3, then the target configures the requiredresources to provide the required quality of service etc. Once thephysical and link layer (L1 & L2) resources have been configured, thetarget HeNB 11-3 sends a handover request acknowledgement message 44 tothe source HeNB 11-2. The handover request acknowledgement message 44includes a transparent container to be sent to the mobile telephone as aradio resource control, RRC, message to perform the handover.

Once the source HeNB 11-2 has received the handover requestacknowledgement 44, or as soon as the transmission of the handovercommand is initiated in the downlink, data forwarding can be performedso that data received at the source HeNB 11-2 is forwarded to the targetHeNB 11-3 to be relayed to the mobile telephone 3.

The target base station 11-3 informs the MME6 in the core network 8 ofthe handover of the user equipment using a path switch request 50. Thepurpose of the path switch request procedure is to request that thedownlink GTP (CPRS tunnelling protocol) tunnel is directed to a GTPtunnel endpoint at the target HeNB 11-3.

An example of a path switch request message 50 is set out in Table 1. InTable 1 the following abbreviations are used: E-RAB is used to indicatethe evolved UMTS Terrestrial Radio Access Network-Radio Access Bearer;IE is used to indicate an information element; GTP-TEID is used toindicate a GPRS tunnelling protocol Tunnel. Endpoint Identifier; E-UTRANCGI is used to indicate the evolved UMTS Terrestrial Radio AccessNetwork Cell Global Identity.

TABLE 1 Seman- As- tics signed Pres- descrip- Criti- Criti- IE/GroupName ence Range tion cality cality Message Type M YES reject eNB UE S1APID M YES reject E-RAB To Be 1 YES reject Switched in DownlinkList >E-RABs 1 to EACH reject Switched in <maxnoof Downlink Item E-RABs>IEs >>E-RAB ID M — >>Transport M — layer address >>GTP-TEID M To deliver— DL PDUs Source MME UE M YES reject S1AP ID E-UTRAN CGI M YES ignoreTAI M YES ignore UE Security M YES ignore Capabilities Cell Access ModeO

In response to the path switch request the MME transmits an updatebearer request 54 or a create session request to the serving gatewaywhich forms part of the MME/S-GW 6 within the core network 8 as shown inFIG. 1, which may in turn relay this request 58 to a packet data networkgateway (not shown).

In the example described above with reference to FIG. 4 the source andtarget HeNB are served by the same serving gateway in the core network8. In this case, as shown in FIG. 5 a modify bearer request message 54is sent from the MME to the serving gateway and from the serving gatewayto the PDN gateway. As shown in FIG. 5 these messages are acknowledgedby the serving gateway and by the PDN gateway. In the example shown inFIG. 6 the source and target base stations (e.g. HeNB 11-2, 11-3) areserved by different serving gateways. In this example, to performserving gateway relocation the MME sends a create session request to thetarget serving gateway. The target serving gateway then sends a modifybearer request message to the PDN gateway. Once this has been done andthe target base station has sent a release resource message to thesource base station the MME sends a delete session request to the sourceserving gateway.

After the down link path is switched in the core network 8, packetsdestined for the mobile telephone 3 are sent to the target HeNB 11-3.The target HeNB 11-3 then sends a X2AP UE Context Release message 46 tothe source HeNB 11-2, to inform the source HeNB 11-2 that the resourcespreviously reserved at the source HeNB 11-2 for the connection to themobile telephone can be released, although any ongoing data forwardingmay continue.

As noted above, the X2AP UE Context Release message 46 is not providedto the HeNB gateway 15. Furthermore, as the target HeNB 11-3 is notconnected to the core network 8 via the HeNB gateway 15, the path switchrequest/response message does not traverse the HeNB gateway 15. Thus,according to embodiments of the invention, the source HeNB 11-2 uponreceipt of the X2AP Context Release message requests release of the UEcontext towards the HeNB gateway 15. Thus, a message 48 from the sourceHeNB 11-2 traverses the HeNB gateway 15, and provides an indication tothe HeNB gateway 15 that the resources and context associated with themobile telephone 3 can be released.

Thus according to embodiments of the invention, for any hand overscenario in which a mobile station 3 is transferred from a cellassociated with a source HeNB 11 coupled to the core network 8 via aHeNB gateway 15 to a cell associated with a target base station that isnot coupled to the HeNB gateway 15, such as the examples shown in FIGS.1, 2 a and 2 b, the source HeNB 11 provides a Context Release indicationmessage 48 that traverses the HeNB gateway 15 and informs the gateway 15that the context and resources associated with the mobile telephone 3can be released.

Modifications and Alternatives

A number of detailed embodiments have been described above. As thoseskilled in the art will appreciate, a number of modifications andalternatives can be made to the above embodiments whilst stillbenefiting from the inventions embodied therein.

While the above discussion relates to the hand over of a user equipmentfrom a source HeNB 11-2 connected to the core network 8 via the HeNBgateway, to a target HeNB 11-3 not connected via the same HeNB gateway15, it is noted that a hand over in the reverse direction (i.e. from abase station not coupled to a HeNB gateway 15 to a target HeNB 11-2coupled to the core network 8 via HeNB GW 15) may also lead to issuesnot currently addressed in the standards. An example of such a handoveris shown in FIG. 7 in which mobile telephone 3 is transferred fromsource HeNB 11-3 to target HeNB 11-2. It will be recognized that otherexample transfers include situations analogous to those shown in FIGS.2a and 2b , in which the handover occurs in the opposite direction tothat shown.

FIG. 8 illustrates the exchange of messages between a target HeNB 11-2connected to the MME 6 of the core network 8 via a HeNB gateway 15 inorder to instruct the core network 8 to switch the termination point ofthe connection to a mobile telephone 3 transferred to the target HeNB11-2. As coordination of the handover to the target HeNB uses the X2interface, the first message relating to the mobile telephone 3 thattraverses the HeNB gateway 15 is the S1-AP Path Switch Request Message50. Thus, this is the first occasion for which a HE associatedsignalling message for the handed over mobile telephone 3 is received atthe HeNB gateway. In order to support this scenario, new functionalitiesmay be provided in the HeNB gateway 15 according to some embodiments ofthe invention. In particular:

-   -   The Mobile Telephone Registration Module 115 of the HeNB gateway        15 may be further configured to allocate the LIE context upon        reception of the S1 Path Switch Request Message.    -   The HeNB gateway 15 may provide a proxy function for subsequent        messages associated with the handed over UE 3 between the HeNB        and the core network 8, including allocating a eNB UE S1AP        ID_(GW) towards the MME 6, and a MME UE S1AP ID_(GW) towards the        HeNB 11-2. The HeNB gateway will exchange the MME S1AP UE ID and        eNB S1AP UE ID values between the global and as necessary        according to the proxy function.    -   The HeNB gateway may be required to include the actual MME UE        S1AP ID value in the S1AP Path Switch Acknowledgement message to        the target HeNB for use in further handovers.

Furthermore, in order to support further X2 based handover procedures,the target HeNB 11-2 should store eNB UE S1AP ID and MME UE S1AP IDvalues associated with the mobile telephone 3 and received from thesource HeNB eNB as part of the X2 based handover procedure.

The target HeNB can then store the MME UE S1AP ID value received fromthe source eNB during handover for use in future handovers, while usingthe MME UE S1AP ID_(GW) value provided by the HeNB GW 15 for all othersignalling towards the HeNB GW 15 and MME 6.

Alternatively, the HeNB GW 15 may provide separate MME UE S1AP ID_(GW)and MME UE S1AP ID2 values to the HeNB 11-2 associated with the mobiletelephone 3. In this case, the HeNB 11-2 will store the MME UE S1AP ID2value for use in future X2 based handover procedures.

In the above embodiments, a mobile telephone based telecommunicationssystem was described. As those skilled in the art will appreciate, thesignalling techniques described in the present application can beemployed in other communications system. Other communications nodes ordevices may include user equipment devices such as, for example,personal digital assistants, laptop computers, web browsers, etc.

In the embodiments described above, the mobile telephone and the HNBeach include transceiver circuitry. Typically this circuitry will beformed by dedicated hardware circuits. However, in some embodiments,part of the transceiver circuitry may be implemented as software run bythe corresponding controller.

In the above embodiments, a number of software modules were described.As those skilled in the art will appreciate, the software modules may beprovided in compiled or un-compiled form and may be supplied to the HNBor to the mobile telephone as a signal over a computer network, or on arecording medium. Further, the functionality performed by part or all ofthis software may be performed using one or more dedicated hardwarecircuits. However, the use of software modules is preferred as itfacilitates the updating of the base stations, gateways, and the mobiletelephones in order to update their functionalities.

The description of the handover process provided above has been givenwith specific reference to home NodeBs however embodiments of theinvention may be applied to other base stations such as eNodeBs or RANbase stations.

While the above discussion relates to a hand over between a HeNB 11-2coupled to a core network via a HeNB gateway 15, and a further HeNB 11-3coupled directly to the core network, it is noted that in otherembodiments of the invention, the hand over may be between two HeNBs 11coupled to the core network via different HeNB gateways.

Various other modifications will be apparent to those skilled in the artand will not be described in further detail here.

The following is a detailed description of the way in which the presentinventions may be implemented in the currently proposed 3GPP standard.Whilst various features are described as being essential or necessary,this may only be the case for the proposed 3GPP standard, for exampledue to other requirements imposed by the standard. These statementsshould not, therefore, be construed as limiting the present invention inany way.

Introduction

During the last RAN3 meeting (RAN3#70bis) meeting, discussion paper [1]highlighted the open issue related to X2 based mobility for HeNB. Asdiscussed in the paper, for the certain scenarios with HeNB GW, afterthe X2 based HO the HeNB GW will be left with hanging UE contexts andrelated resources, RAN3 acknowledged the issue and it was decided todiscuss further and find a solution for this problem. This discussionpaper analyzes the issue and proposes potential solutions.

2 Description

It was acknowledged that the problem will happen during the X2 HO in twocases:

-   -   (a) The source HeNB is connected via the HeNB GW and target HeNB        connected directly to the MME.    -   (b) The source HeNB and target HeNB are connected to different        HeNB GWs.

Since the source HeNB is connected behind the HeNB GW, therefore twopair of UE associated connection is established, one between HeNB andHeNB GW and another between HeNB GW and MME. The mapping of these twoLIE associated signalling connected for the same UE is performed by theHeNB GW. Therefore, UE context and related resources are allocated bothat the HeNB and the HeNB GW.

During the X2 based HO, the target HeNB explicitly releases the UEContext at the source HeNB using the X2AP UE Context Release procedure.On the other hand, since S1AP C Plane message i.e. S1AP Path SwitchRequest/Response message does not transverse through the HeNB GWtherefore, the HeNB GW does not have any means to understand that theTIE has been handed over (via X2) to the other HeNB. As a result, the UEcontext information and related resources assigned by the HeNB GW willkeep hanging. Three possible solutions have been discussed during thelast RAN3 meeting.

-   -   1. The source HeNB GW releases the UE context by itself    -   2. The source HeNB GW releases the UE context as the request        from the source HeNB    -   3. The source HeNB GW releases the HE context as the command        from the MME

Solution 1 considered as an inadequate because this solution canpossibly address (further investigation needed) the deployment scenariowhere HeNB GW S1-U plane transverse through the HeNB GW, noting thatS1-U concentration in the HeNB GW is optional. Solution 3 can work butseen as significant changes for the MME behaviour to address only thisparticular use case. Therefore, it is reasonable to investigate more onthe solution 2 which does not have any impact on the MME.

The basic essence of solution 2 is that source HeNB requests the releaseof UE context towards the HeNB GW. There are two possible options tohandle this.

Option 1: Re-use the Existing S1AP UE Context Release Request—eNBInitiated Procedure

The benefit of option 1 is that there is no need to define any newprocedure. On the other hand, there are some drawbacks for thissolution. Firstly, this procedure is only meant to be used for abnormalcases (as per TS 36.413) and not for the normal X2 HO. secondly,additional signalling during X2HO since HeNB has to trigger the releaseof UE context towards the HeNB GW. Thirdly, the HeNB GW has to lookevery S1AP UE CONTEXT RELEASE REQUEST from the HeNB and then decidewhether this message to be sent to MME (for the existing use case ofthis procedure) or terminate at the HeNB GW in case it is triggered dueto X2 based HO. And, finally HeNB GW need to trigger UE Context Release(MME initiated) procedure (class 1) after receiving S1AP UE CONTEXTRELEASE REQUEST from the HeNB, means more signalling.

Option 2: Define a New Class 2 Procedure Along the Line of X2AP UEContext Release Indication Procedure

The second easy mechanism is to define a new class 2 procedure along theline of X2AP UE Context Release procedure. The source HeNB will triggerthe procedure upon reception of X2AP UE Context Release from the targetHeNB. The HeNB GW behaviour in this case would be simple because the theHeNB does not need to check the cause of every UE CONTEXT RELEASEREQUEST message. Of course there is disadvantage that HeNB will need toterminate UE associated signalling message which is an exception. As analternative non UE associated signalling could be also used. Based onthe above evaluation, our preference is option 2 because it requiresless signalling and less HeNB/HeNB GW implementation complexity.

Proposal 1 : NEC Proposes to Agree on Option 2 in Order to Resolve theUE Context Release Issue at the HeNB GW.

The necessary changes in TS 36.413 and TS 36.300 is as described below(Annex). In case of agreement, NEC is happy to provide the necessaryCRs.

3 Conclusion and Proposals

Proposal 1: NEC Proposes to Agree on Option 2 in Order to Resolve the UEContext Release at the HeNB GW issue.

4 References

[1] TS 36,300 E-UTRAN stage-2

[2] R3-110108 UE Context Release in the source HeNB GW

Annex A.1

This section describes the necessary stage-2/3 changes needed in thespecification.

===Changes for Ts 36.413===

8. 3.x UE Context Release Indication

8. 3.x.1 General

The UE Context Release indication procedure is initiated by the eNB tosignal to indicate the source MME that UE context shall be released.

The procedure uses UT-associated signalling.

8. 3.x.2 Successful Operation

The UE Context Release Indication procedure is initiated by the eNB. Bysending the UE CONTEXT RELEASE INDICATION message the target eNB informsthe MME of X2 Handover success and triggers the release of resources.This procedure is only triggered by the eNB if different values for MMEUE S1AP ID and MME UE S1AP ID2 are assigned by the MME.

Upon reception of the UE CONTEXT RELEASE message, the MME may release UEContext and related resources associated to the UE context.

8. 3.x.3 Unsuccessful Operation

Not applicable.

8. 3.x.4 Abnormal Conditions

Not applicable.

Next Change

9.1.1.5 UE CONTEXT RELEASE Indication

This message is sent by the eNB to the MME to indicate that resourcescan be released.

Direction: eNB→MME.

IE type and Semantics Assigned IE/Group Name Presence Range referencedescription Criticality Criticality Message Type M 9.2.13 YES ignore eNBUE S1AP ID M eNB UE X2AP ID Allocated at YES reject 9.2.24 the sourceeNB MME UE S1AP ID M eNB UE X2AP ID Allocated at YES reject 9.2.24 thetarget eNB===Changes for TS 36.300===4.6.2 Functional Split

The HeNB hosts the same functions as an eNB as described in section 4.1,with the following additional specifications in case of connection tothe HeNB GW:

-   -   Discovery of a suitable Serving HeNB GW;    -   A HeNB shall only connect to a single HeNB at one time, namely        no S1 Flex function shall be used at the HeNB:        -   The HeNB will not simultaneously connect to another HeNB GW,            or another MME.    -   The TAC and PLMN ID used by the HeNB shall also be supported by        the HeNB GW;    -   Selection of an MME at UE attachment is hosted by the HeNB GW        instead of the HeNB;    -   HeNBs may be deployed without network planning. A HeNB may be        moved from one geographical area to another and therefore it may        need to connect to different HeNB GWs depending on its location.    -   On completion of X2 HO, release of TIE Context and triggering        the UE Context Release procedure.

Regardless of HeNB GW connection:

-   -   The HeNB may support the LIPA function. See section 4.6.5 for        details.

The HeNB GW hosts the following functions:

-   -   Relaying UE-associated S1 application part messages between the        MME serving the UE and the HeNB serving the UE;    -   Terminating non-UE associated S1 application part procedures        towards the HeNB and towards the MME. Note that when a HeNB GW        is deployed, non-UE associated procedures shall be run between        HeNBs and the HeNB GW and between the HeNB GW and the MME.    -   Optionally terminating S1-U interface with the HeNB and with the        S-GW.    -   Supporting TAC and PLMN ID used by the HeNB.    -   X2 interfaces shall not be established between the HeNB GW and        other nodes.    -   Termination of the UE Context Release procedure and releasing        the UE Context based on the indication from the HeNB.

A list of CSG Ms may be included in the PAGING message. If included, theHeNB GW may use the list of CSG IDs for paging optimization.

In addition to functions specified in section 4.1, the MME hosts thefollowing functions:

-   -   Access control for UEs that are members of Closed Subscriber        Groups (CSG):        -   In case of handovers to CSG cells, access control is based            on the target CSG provided to the MME by the serving            E-UTRAN.    -   Membership Verification for UEs handing over to hybrid cells:        -   In case of handovers to hybrid cells Membership Verification            is triggered by the presence of the Cell Access Mode and it            is based on the target CSG ID provided to the MME by the            serving E-UTRAN.    -   CSG membership status signalling to the target E-UTRAN in case        of attachment/handover to hybrid cells and in case of the change        of membership status when a UE is served by a CSG cell or a        hybrid cell.    -   Supervising the eNB action after the change in the membership        status of a UE.    -   Routing of handover messages and MME configuration transfer        messages towards HeNB GWs based on the TAI contained in these        messages.        -   NOTE: The MME or HeNB GW should not include the list of CSG            IDs for paging when sending the paging message directly to            an un-trusted HeNB or eNB.    -   The MME may support the LIPA function with HeNB. See details of        this support in section 4.6.5.        Annex A.2        9.1.5.9 PATH SWITCH REQUEST ACKNOWLEDGE

This message is sent by the MME to inform the eNB that the path switchbeen successfully completed in the EPC.

Direction: MME→eNB.

IE type and Semantics Assigned IE/Group Name Presence Range referencedescription Criticality Criticality Message Type M 9.2.1.1 YES rejectMME UE S1AP ID M 9.2.3.3 YES ignore eNB UE S1AP ID M 9.2.3.4 YES ignoreUE Aggregate O 9.2.1.20 YES ignore Maximum Bit Rate E-RAB To Be 0 . . .1 YES ignore Switched in Uplink List  >E-RABs 1 to EACH ignore  Switchedin <maxnoofE-  Uplink Item IEs RABs>   >>E-RAB ID M 9.2.1.2 —  >>Transport M 9.2.2.1 —   Layer Address   >>GTP-TEID M 9.2.2.2 — E-RABTo Be O E-RAB List a value for E- YES ignore Released List 9.2.1.36 RABID shall only be present once in E-RAB To Be Switched in Uplink ListIE + E-RAB to Be Released List IE Security Context M 9.2.1.26 One pairof YES reject {NCC, NH} is provided Criticality O 9.2.1.21 YES ignoreDiagnostics MME UE S1AP ID 2 O 9.2.3.3 This IE YES reject indicates theMME UE S1AP ID assigned by the MME Range bound Explanation maxnoofE-RABsMaximum no. of E-RABs for one UE. Value is 256.

This application is based upon and claims the benefit of priority fromUnited Kingdom patent application No. 1102883.4, filed on Feb. 18, 2011,the disclosure of which is incorporated herein in its entirety byreference.

What is claimed is:
 1. A method performed by a source base station, themethod comprising: initiating a handover of a mobile device from thesource base station to a target base station via an X2 interface betweenthe source base station and the target base station; receiving, throughthe X2 interface, a UE Context Release message from the target basestation to inform of successful handover to the source base station, theUE Context Release message including information, allocated at thetarget base station, identifying the mobile device; and when the sourcebase station is connected to a base station gateway, sending a UEContext Release Request message, to indicate that the base stationgateway may release resources related to a context associated with themobile device.
 2. A method performed by a base station gateway, themethod comprising: receiving, from a source base station, when thesource base station is connected to the base station gateway andfollowing a successful handover of a mobile device to the source basestation via an X2 interface between the source base station and a targetbase station, a UE Context Release Request message to indicate that thebase station gateway may release resources related to a contextassociated with a mobile device; and releasing the context associatedwith the mobile device in response to receiving the UE Context ReleaseRequest message from the source base station.
 3. A source base stationcomprising: a processor; and a transceiver circuit, wherein theprocessor is configured to: initiate a handover of a mobile device froma source base station to a target base station via an X2 interfacebetween the source base station and the target base station; control thetransceiver circuit to receive, at the source base station, through theX2 interface, a UE Context Release message from the target base stationto inform of successful handover to the source base station, the UEContext Release message including information, allocated at the targetbase station, identifying the mobile device; and control the transceivercircuit to, when the source base station is connected to a base stationgateway, to send a UE Context Release Request message, to indicate thatthe base station gateway may release resources related to a contextassociated with the mobile device.
 4. A base station gateway comprising:a processor; and a transceiver circuit, wherein the processor isconfigured to: receive, from the source base station according to claim3, when the source base station is connected to the base station gatewayand following a successful handover of a mobile device to the sourcebase station via an X2 interface between the source base station and atarget base station, a UE Context Release Request message to indicatethat the base station gateway may release resources related to a contextassociated with a mobile device; and release the context associated withthe mobile device in response to receiving the UE Context ReleaseRequest message from the source base station.